A. Field of the Invention
The present invention relates to releasable packaging for hot-melt pressure sensitive adhesive compositions and to a preform of the release packaging. More particularly, the present invention relates to a method for releasably packaging a hot-melt pressure sensitive adhesive in a continuous form-fill-seal mode. The present invention is useful because it permits a hot-melt pressure sensitive adhesive composition to be releasably packaged at high speed and in a variety of sizes to suit a customer's needs.
B. Background
Hot-melt adhesives are adhesives that are tacky when applied in the "hot-melt" or molten state. At room temperature, all hot-melt adhesives are solids. Hence, as a practical matter, all hot-melt adhesives are sold as solids, e.g., rigid blocks.
Hot-melt pressure sensitive adhesives ("pressure sensitives") are the class of hot-melt adhesives that are very tacky to the touch even at room temperature. As a solid, pressure sensitives create an adhesive bond upon contact with a substrate without the introduction of heat. These are desirable adhesive properties. However, these properties create a packaging problem. The pressure sensitive adheres to itself and to all traditional hot-melt packaging at room temperature. Current packaging for pressure sensitive includes the Hot-Flo drums of Grief Brothers, the silicone release coated cardboard folding boxes of Menasha Paper Company, the powdered plastic water immersed disposable multi-cavity trays, and H. B. Fuller's wax co-extrusion.
Packaging for pressure sensitives must provide the pressure sensitive in a form that can be put into the customer's glue pots for melting prior to application. All of the aforementioned packaging, except the Hot-Flo drums of Grief Brothers, are of sizes that provide a rigid block of pressure sensitive adhesive which can be hand inserted into the glue pots. With the Hot-Flo drums, a drum unloader pre-melts the solid pressure sensitive in the drum, and once molten, pipes it into the glue pots. The expense of using a drum unloader to heat, melt and dispense a drum of adhesive can be absorbed by and be efficient for only the largest users. These capital considerations make this form uncommon, even though the packaging costs only about $0.05 per lb. It is an object of the present invention to provide inexpensive packaging for pressure sensitives that allows them to be handled in sizes that are less than a drum. A second type of packaging for hot-melt pressure sensitive adhesives is the folding silicone lined carton of Menasha. Menasha's folding silicone lined cartons are expensive, costing about $0.19 per lb for a 21/2 lb brick. Moreover, they are very labor intensive to both fold and fill. For example, the Menasha 21/2 lb. brick carton has 26 fold lines. Further, the molten pressure sensitive adhesive that is filled into the Menasha carton must fully solidify before being master-packed and transported. This means that for a 21/2 brick, a great deal of cooling time is required. These factors drive the packaging costs to well over $0.20 per lb. In addition, the purchaser of any pressure sensitive that is supplied in a silicone lined carton must handle a "naked" brick of the adhesive when inserting it into his glue pot. This can be dangerous.
The naked brick is very tacky and has been known to adhere to the hand while being eased into a glue pot containing the molten material. Use of the other hand to unstick the naked brick, which would have molten glue on the other end, has caused severe burns to the saving hand of glue pot operators. Another problem associated with use of the silicone lined carton is that the user must dispose of a large number of empty cartons which are not recyclable and create a voluminous amount of refuse.
It is an object of the present invention to provide a packaging for pressure sensitives that allows the pressure sensitive adhesive to be safely handled in its solid form without tack. It is another object of the present invention to provide a packaging for pressure sensitives that produce a minimal amount of refuse.
An alternative packaging system for pressure sensitives is the multi-cavity plastic immersion tray. These multi--cavity trays, which resemble large sized one piece ice cube trays, provide improved handling characteristics over the silicone lined cartons. The multi-cavity trays are first powdered to reduce handling surface tackiness. They are then immersed in a cooling trough as they are filled within a molten pressure sensitive by a metered extrusion head. The filled trays are conveyed in the fluid until the pressure sensitive solidifies into a rigid brick and then cools to a transportable temperature. Finally, the solidified adhesive in the cavities are top-dusted and master-packed for shipment. The customer removes the bricks by inverting and deforming the cavity. The powdered bricks are less tacky on the surface than Menasha-type bricks, but are inserted into the glue pots the same way because they are less labor intensive and quicker to fill. The powdered bricks are commonly smaller bricks than the "naked" bricks, i.e., about 1 lb instead of 21/2 lb.
The problem with the multi-cavity trays is the necessity of the cooling/conveyance system which is unique to pressure sensitives and requires huge capital investment by the producer. Such an investment is typically only made by the larger adhesive manufacturers. It is an object of the present invention to provide a packaging system that is both inexpensive and that avoids the conveyance of the packaged product in a liquid cooling system.
Another problem with the multi-cavity trays is that they must be both thick and strong enough to avoid melting when filled, yet dissipate heat quickly enough to allow full cooling by the line's end. Such trays are costly. Investment in a die to form the trays can also run $40,000. These expenses end up driving the packaging costs of this process up to about $0.15 per lb. Further, the trays are typically not recycled back to the manufacturer and again produce a voluminous amount of waste for the end user. It is an object of the present invention to eliminate this voluminous packaging waste.
Another process for packaging a pressure sensitive is co-extrusion. In co-extrusion, wax or some tack-free coating is co-extruded around a short core ("pillow") of pressure sensitive adhesive glue. This process makes the extruded pillow form non-tacky, and hence it can be packaged by more traditional methods. These short pinched "pillows" of pressure sensitive are easily scoop loaded into the customer's glue pots. A problem with the co-extrusion process is that a large capital investment is needed to purchase the co-extrusion equipment and the equipment is complex to operate. It is an object of the present invention to develop a packaging for pressure sensitives that does not require the large capital investment associated with co-extrusion equipment.